[aur-general] How should *-devel packages generally be handled?

[Ng Oon-Ee]

Package foo exists in [extra], and foo-devel in the AUR.

foo-devel is obviously based off unstable tarball releases (otherwise it
would be foo-git, foo-svn, foo-hg or similar).

So let's say foo is at version 4.0 (stable), should foo-devel stay at
3.9 (the last beta/rc/unstable release) or update to 4.0?

Just a general question. My gnucash-devel package is currently pretty
much identical to the one in [extra], and it does seem a bit unnecessary
because the project itself does not currently have unstable releases.